On 06/20/2017 05:21 PM, Dawid Zamirski wrote: > On Tue, 2017-06-20 at 17:03 +0200, Erik Skultety wrote: >> Since we have a number of places where we workaround timing issues >> with >> devices, attributes (files in general) not being available at the >> time >> of processing them by calling usleep in a loop for a fixed number of >> tries, we could as well have a utility function that would do that. >> Therefore we won't have to duplicate this ugly workaround even more. >> >> This is a prerequisite for >> https://bugzilla.redhat.com/show_bug.cgi?id=1463285. >> >> Signed-off-by: Erik Skultety <eskultet@xxxxxxxxxx> >> --- >> src/libvirt_private.syms | 1 + >> src/util/virfile.c | 36 ++++++++++++++++++++++++++++++++++++ >> src/util/virfile.h | 2 ++ >> 3 files changed, 39 insertions(+) >> >> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms >> index c1e9471c5..53878a30f 100644 >> --- a/src/libvirt_private.syms >> +++ b/src/libvirt_private.syms >> @@ -1698,6 +1698,7 @@ virFileStripSuffix; >> virFileTouch; >> virFileUnlock; >> virFileUpdatePerm; >> +virFileWaitForAccess; >> virFileWrapperFdClose; >> virFileWrapperFdFree; >> virFileWrapperFdNew; >> diff --git a/src/util/virfile.c b/src/util/virfile.c >> index 6bbcc3d15..0b1a91699 100644 >> --- a/src/util/virfile.c >> +++ b/src/util/virfile.c >> @@ -4164,3 +4164,39 @@ virFileReadValueString(char **value, const >> char *format, ...) >> VIR_FREE(str); >> return ret; >> } >> + >> + >> +/** >> + * virFileWaitForAccess: >> + * @path: absolute path to a sysfs attribute (can be a symlink) >> + * @ms: how long to wait (in milliseconds) >> + * @tries: how many times should we try to wait for @path to become >> accessible >> + * >> + * Checks the existence of @path. In case the file defined by @path >> + * doesn't exist, we wait for it to appear in 100ms (for up to >> @tries times). >> + * >> + * Returns 0 on success, -1 on error (ENOENT is fine here). >> + */ >> +int >> +virFileWaitForAccess(const char *path, size_t ms, size_t tries) >> +{ >> + errno = 0; >> + >> + /* wait for @path to be accessible in @ms milliseconds, up to >> @tries */ >> + while (tries-- > 0 && !virFileExists(path)) { >> + if (errno != ENOENT) { >> + virReportSystemError(errno, "%s", path); >> + return -1; >> + } else if (tries == 10) { >> + virReportError(VIR_ERR_INTERNAL_ERROR, >> + _("Failed to access '%s' after %zu >> tries"), >> + path, tries); >> + return -1; >> + } else { >> + VIR_DEBUG("Failed to access '%s', re-try in %zu ms", >> path, ms); >> + usleep(ms * 1000); >> + } >> + } >> + >> + return 0; >> +} > > Just FYI, there's another way to address it by calling udevadm settle > before and after "touching" a block device, libguestfs is using this > approach and it works very well: > > https://github.com/libguestfs/libguestfs/search?utf8=%E2%9C%93&q=udev_s > ettle&type= Does it? udevadm settle waits for all the events to be processed, not just the one that we want. The wait time would be unpredictable IMO. Michal -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
